1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus and a multi charged particle beam writing method. For example, the present invention relates to a method for achieving high accuracy in writing with multiple beams.
2. Description of Related Art
The lithography technique that advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer, etc. with an electron beam.
As an example using the electron beam writing technique, there is a writing apparatus using multiple beams (multi-beams). Since it is possible for a multi-beam writing apparatus to perform irradiation with multiple beams at a time, throughput can be greatly increased compared with the case of writing using a single electron beam. In such a writing apparatus of a multi-beam system, for example, multiple beams are formed by letting an electron beam emitted from an electron gun assembly pass through a mask with a plurality of holes, blanking control is performed for each beam, and each of unblocked beams is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample” (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2006-261342).
In such a writing apparatus of the multi-beam system, irradiation of a plurality of beams is performed at a time, and a pattern is written by combining “beam on” and “beam off” by blanking control as described above. Regarding the writing apparatus of the multi-beam system, there is a concern about yield (generation of a defective beam) because of structural complexity for forming and controlling a plurality of beams. For example, when the beam-off control cannot be performed, a defective beam being continuously “beam on” may be generated. In addition, there is a case of generating a defective beam which does not have a specified amount of beam current or whose dose cannot be controlled within a predetermined irradiation time period even if the beam-off control can be performed. When a defective beam of this kind exists, a problem occurs in that a desired pattern is not written or desired writing accuracy is not obtained even though writing is performed.